These studies represent a continuation of studies on the structural and control properties of a group of biotinyl-enzymes. The project involves mainly methylmalonyl-CoA--oxalacetate transcarboxylase from the propionic acid bacteria and pyruvate carboxylase from a variety of sources. Electron microscopy, immunological studies and cross linking procedures will be employed to determine the basis of the apparent homology of parts of the central and outside subunits of transcarboxylase, the nature and location of the sites which link two types of subunits to each other, and the location of the biotin sites in transcarboxylase. Many of the same procedures will be used to establish the quarternary structure of pyruvate carboxylases from yeast, Pseudomonas citronellolis, rat and chicken liver and to investigate the location of the various portions of the catalytic sites in relationship to overall structure. The regulation of the animal enzymes will also be investigated especially with respect to their role in normal and abnormal metabolism.